This invention relates to a system for interfolding sheets, such as paper toweling, and more particularly to an interfolding system which is capable of forming a discontinuity in a stack of interfolded sheets to enable the stack to be separated at predetermined locations according to a desired sheet count.
A stack of interfolded sheets can be formed in different ways. In one system, a pair of webs are severed into sheets, which are then brought together in a staggered relationship. The sheets are supplied to an interfolder, which is operable to form the staggered sheets into an interfolded stack. In another system, commonly known as a lapping interfolder, a single web is cut into successive sheets which :are then fed through a pair of retard rolls, which are operable to create an overlap in the successive sheets. The overlapped sheets are then supplied to a pair of folding rolls which fold the lapped sheets into an interfolded stack.
From the discharge of the folding rolls, a predetermined number of the sheets are separated for further processing, such as for packaging in a sleeve-type package or the like and then subsequent severing of the sheets to length. Various types of mechanisms are known to separate the stack to a desired sheet count. Examples of such mechanisms are disclosed in Hathaway U.S. Pat. Nos. 4,717,135 and 4,721,295; Couturier U.S. Pat. No. 4,770,402; Stemmler U.S. Pat. No. 5,088,707, and White U.S. Pat. No. 6,165,116. The disclosures of such patents are hereby incorporated by reference. The White patent discloses an arrangement for forming a gap in one of two streams of sheets supplied to the interfolding rolls, to create a discontinuity in the interfolded stack. The discontinuity in the stack facilitates separation of a portion of the stack from the remainder of the stack, for subsequent processing. In White, the interruption in the sheet supply occurs in one of the streams of sheets upstream of the interfolding rolls. Stemmler U.S. Pat. No. 5,088,707 and Hathaway U.S. Pat. No. 4,717,135 also show systems for manipulating the streams of sheets upstream of the interfolder, for creating a separation in the stack. Couturier U.S. Pat. No. 4,770,402 discloses a separator located downstream of the interfolding rolls for counting and separating a clip of sheets according to a desired sheet count.
It is an object of the present invention to provide an apparatus and method for creating a discontinuity or separation in a stack of interfolded sheets formed using a lapping interfolder, in which the discontinuity or separation is formed upstream of the interfolding rolls. Another object of the invention is to provide such an apparatus and method which can be carried out by modifying operation of existing components of a lapping interfolder. Yet another object of the invention is to provide such an apparatus and method which is capable of creating a discontinuity in a stack of interfolded sheets, without any significant reduction in the speed of operation of the interfolder. A still further object of the invention is to provide such an apparatus and method which is relatively simple in its components and operation, yet which can be operated to reliably form a discontinuity or interruption in a stack of interfolded sheets.
In accordance with the present invention, a web is supplied to a severing arrangement, which functions to sever the web into separate sheets which are then directed toward an interfolder, which may be in the form of a pair of counter-rotating interfolding rolls. At a location downstream of the severing arrangement and upstream of the interfolding rolls, the severed sheets are supplied to a nip defined by a pair of counter-rotating rolls. In one form, the counter-rotating rolls between the severing arrangement and the interfolding rolls may be in the form of conventional retard rolls, which are operated at a speed slower than the speed at which the successive severed sheets are supplied from the severing arrangement. In conventional operation, the retard rolls function to create an overlap of successive sheets, and the overlapped sheets are then supplied from the retard rolls to the nip of the interfolding rolls.
To create an interruption or discontinuity in the interfolded sheets formed by the interfolding rolls, the interfolding rolls a pair of rolls upstream of the interfolding rolls, which may be the retard rolls, are operated at a differential speed to advance the trailing edge of a downstream sheet out of overlapping relationship with the leading edge of the adjacent upstream sheet. The speed differential in operation of the interfolding rolls and the upstream rolls, which may be the retard rolls, is preferably carried out by selectively slowing the speed of rotation of the retard rolls while maintaining the speed of operation of the interfolding rolls. In this manner, the downstream sheet is advanced through the nip of the interfolding rolls at a speed greater than the speed at which the next upstream sheet is advanced by the retard rolls toward the nip of the interfolding rolls. The speed of operation of the retard rolls is selected such that, when the leading edge of the upstream sheet reaches the nip of the interfolding rolls, the trailing edge of the downstream sheet has been advanced through the nip of the interfolding rolls ahead of the leading edge of the upstream sheet, to eliminate the overlapping relationship between the downstream and upstream sheets. As a result, the downstream sheet is advanced through the nip of the interfolding rolls prior to discharge of the leading edge of the upstream sheet from the nip of the interfolding rolls. In this manner, the upstream and downstream sheets are not interfolded, to create the desired interruption or discontinuity in the stack of sheets to facilitate separation of the sheets for further processing. After the downstream sheet and the upstream sheet have been separated in this manner, the speed of rotation of the retard rolls is returned to normal, to advance successive sheets toward the interfolding rolls in a conventional manner. The prior slowing in the speed of operation of the retard rolls causes an increase in the degree of overlap between the upstream sheet and the next adjacent upstream sheet, which are then fed together by the retard rolls toward the interfolding rolls, and interfolded on top of the end panel of the downstream sheet to initiate formation of a new group of sheets in the stack. Conventional operation of the lapping interfolder then continues in this manner, until a desired number of sheets have been interfolded in the new group and a discontinuity or interruption in the stack is then subsequently formed, to separate the group of sheets from the next group of sheets to be formed in the stack.
The invention contemplates an apparatus that functions in the manner described above so as to create an interruption or discontinuity in a stack of interfolded sheets, as well as a method of operating a sheet processing system so as to create an interruption or discontinuity in a stack of interfolded sheets, substantially in accordance with the foregoing summary.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.